1. Field of the Invention
The present invention relates to a high-temperature high-pressure processing method for semiconductor wafers, and an anti-oxidizing body for the method.
2. Description of the Related Art
Copper (Cu) has been recently highlighted as a wiring material for a semiconductor device, and electrolytic plating occupies the mainstream as a film forming method thereof.
On the other hand, a finer wiring has been steadily progressed, that is, a level of 0.18xcexc has been made practical, further, 0.15xcexc or 0.13xcexc, and a further finer level has been tried.
However, with the fineness, it is difficult to positively embed a material deeply into a hole in a wiring film. Defects such as large and small voids sometimes occur within the wiring. Attention has now been paid to the utility of high pressure as a method for forming a sound wiring film without voids.
The utilization of high pressure is described in detail, for example, in xe2x80x9cApplication of HIP to ULSI Fabrications (A Challenge to Sub-Quarter Micron World)xe2x80x9d (1999), Proc. Int. Conf On HIP Beijing, Chinese MRS, p276-281, T. Fujikawa et. al.
In the aforementioned process, argon gas is normally used as a pressure medium, and for example, for the soundness of Cu film-formed by electrolytic plating, temperature above 350xc2x0 C. and pressure above 120 MPa are necessary.
Argon gas of 99.998% used normally contains oxygen of about 0.2 ppm and water of about 2 ppm.
Where pressure is 120 MPa, for example, the quantity of oxygen corresponds to that oxygen of about 0.02% is contained in argon gas in atmospheric pressure.
It has been found therefore that when heated to 350xc2x0 C. at such a high pressure atmosphere as described, the surface of the Cu film is oxidized to an industrially injurious level by the presence of oxygen and water in argon gases.
Sometimes, the surface of a semiconductor wafer becomes discolored into black purple to lose luster, after the semiconductor wafer has been processed under high-temperature high-pressure. The present inventors have analyzed in ingredient the aforesaid surface and found that a large quantity of oxygen was detected. It was therefore found that the discoloring was caused by oxidization. It was found by SEM observation of the broken surface of the semiconductor wafer that the Cu wiring film was so sound that no void was observed.
When the surface of the semiconductor wafer is oxidized, the hardness is changed, resulting in variation of a film thickness in post step, which is CMP (chemomechanical polishing for flattening the surface). This greatly influences on the production yield of an expensive semiconductor chip. Where the oxidized contamination is great, it adversely influences on an electric specific characteristic itself Accordingly, it is extremely important that in high-temperature high-pressure processing, the surface of the semiconductor wafer not be oxidized.
It is also contemplated that for preventing the surface of the wafer from being oxidized in high-temperature high-pressure processing, for example, argon gas of 99.9999% super-high purity is used.
However, the cost of the argon gas of 99.9999% is about 7 times than that of argon gas of 99.998%, materially increasing the cost in high-temperature high-pressure processing.
Further, even the argon gas of super-high purity, since some quantity of impurity are accumulated in the argon gas every high-temperature high-pressure processing, it is difficult to recycle-use the argon gas, which results in wasteful use of resources and increase in cost.
It is an object of the present invention to provide a high-temperature high-pressure processing method capable of preventing surface contamination of a semiconductor wafer not depending on even gas of super-high purity, and an anti-oxidizing body used for the method.
According to the present invention, there is provided a high-temperature high-pressure processing method in which a semiconductor wafer is charged into a pressure vessel to process it under the gas atmosphere of high-temperature high-pressure, wherein an anti-oxidizing body (an oxygen getter member) formed of a material having properties in which oxygen is apt to diffuse into interior is subjected to high-temperature high-pressure processing in the state that the anti-oxidizing body is arranged within the pressure vessel. In this case, since the anti-oxidizing body takes in oxygen within the pressure vessel, it is possible to prevent oxygen within the pressure vessel from being reduced to oxidize the surface of a semiconductor wafer in the high-temperature high-pressure processing.
Materials for the anti-oxidizing body are preferably titanium or a titanium alloy or zirconium or a zirconium alloy.
Preferably, the high-temperature high-pressure processing is carried out in the state that semiconductor wafers and a plate-like anti-oxidizing body formed substantially in the same shape as viewed in plane as the semiconductor wafers are mixed and supported on a wafer support capable of supporting a plurality of semiconductor wafers.
In this case, when the semiconductor wafers are supported on the wafer support, the anti-oxidizing body along with the semiconductor wafers may be supported on the wafer support. Therefore, the anti-oxidizing body can be arranged within the pressure vessel easily. Preferably, the semiconductor wafers are film-formed in Cu.
The anti-oxidizing body according to the present invention is featurized in that a material having properties in which oxygen is apt to diffuse into interior is formed to be a plate-like having substantially the same shape as viewed in plane as the semiconductor wafer.
The anti-oxidizing body is made substantially the same shape as the semiconductor wafer whereby the anti-oxidizing body can be handled similarly to the semiconductor wafer. That is, it is possible to transport and support the anti-oxidizing body by means of a unit for transporting and supporting the semiconductor wafer, facilitating the handling thereof.
Preferably, the anti-oxidizing body is applied with mirror polishing processing, and preferably, the whole or a part of one surface out of both surfaces of the plate is applied with coating. Where the anti-oxidizing body is handled similarly to the semiconductor wafer, it is unavoidable that the former comes in contact with the unit for transporting and supporting the semiconductor wafer. In this case, when the anti-oxidizing body comes in contact with the unit as described, dust sometimes occurs. Particularly, in an anti-oxidizing body made of metal such as titanium, the semiconductor wafer is possibly contaminated in metal. Application of coating prevents occurrence of dust caused by the contact. Coating is preferably coating of an insulator such as ceramic coating.